I don't expect we'll see one-by-one updates. It just doesn't make sense, from an efficiency standpoint, to update every time a restaurant is added. Once all the contract negotiations are done, we'll get one big update.
An exception to this thinking *might* be Disney dining. When I first made my January ADRs, at 180 out, I was told specifically that as of now, Planet Hollywood and Teppan Edo are not on the plan, but that negotiations were ongoing. When I called to make a change from Rose & Crown to Tutto Italia, I was told that TI is a 1TS credit meal on the dining plan. So either the CM was erroneously giving me this year's information, or the Disney dining system is getting updates as they happen even though the official brochure update won't come until the entire list is final. I'll test this theory some time next week, assuming the rumors about the P&PP announcement coming this week are accurate, because I have a couple more changes to make and one of them is to book a restaurant that isn't on the publicly released dining plan list yet.
ETA: Until we see the final list, I'm keeping my fingers crossed for Tutto Italia, Teppan Edo and Tokyo Dining.